2003 mustang no crank no start

Make sure the battery has a full charge and connections all good. Your saying the starter motor won't crank the engine? Note the diagram. Unplug the starter relay, use a jumper wire between cavities 30 and 87 in the diagram, terminal 30 is hot all the time and fuse protected, that is the switch side of relay, left side in diagram. The starter motor should crank the engine. If you try that, make sure transmission is in park or neutral and parking brake is set. Make sure the vehicle can't move. If it cranks with jumper but other wise not, have to check control side of relay, that side needs voltage and ground. In the diagram, top wire is voltage, bottom wire is ground. The voltage goes hot with the key in the crank position and is wired through transmission range sensor.

Thanks. It did start. But i dont understand what you mean by "have to check control side of relay, that side needs voltage and ground".